1 List of United States cities by population. ^ 2  Population projection is that of the entity known since 2016 as Ciudad de MÃ©xico and previously as the Distrito Federal. ^  Population estimate is that of the Toronto census division, which consists solely of the City of Toronto.
Lens (optics) For other uses, see Lens. A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (elements), usually arranged along a common axis.
noun, plural lenses. 1. a piece of transparent substance, usually glass, having two opposite surfaces either both curved or one curved and one plane, used in an optical device in changing the convergence of light rays, as for magnification, or in correcting defects of vision. 2. a combination of such pieces.